Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, medium- or large-sized devices, such as vehicles, use a medium- or large-sized battery pack having a plurality of battery cells electrically connected with each other because high output and large capacity are necessary for the medium- or large-sized devices.
Preferably, the medium- or large-sized battery pack is manufactured with small size and small weight if possible. For this reason, a plate-shaped battery cell, such as a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a unit cell of the medium- or large-sized battery pack. Especially, much interest is currently generated in the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member (a battery case).
In the plate-shaped battery, the electrode terminals generally may protrude from the outer surface of the battery on the same plane. Alternatively, one of the electrode terminals may protrude from the outer surface of the battery, and the battery case of the battery may serve as the other electrode terminal. In the former case, however, the cathode terminal and the anode terminal are positioned on the same plane, and therefore, the possibility of short circuits is high during the handling of the battery or during the manufacturing of a battery pack. In the latter case, on the other hand, the possibility of short circuits is higher. In addition, most of the battery case must be insulated excluding the region used as the electrode terminal, whereby the process is troublesome and complicated.
For this reason, there have been developed structures in which the electrode terminals protrude from different regions of the outer surface of the battery. One of them is a battery structure in which the electrode terminals are formed at the opposite ends of the battery. An example is illustrated in FIGS. 1 and 2, which are a perspective view and a vertical sectional view illustrating a conventional representative pouch-shaped battery.
Referring to these drawings, a pouch-shaped battery 10 is constructed in a structure in which two electrode leads (electrode terminals) 11 and 12 protrude from the upper and lower ends of a battery cell 13, respectively, while the electrode leads are opposite to each other. The electrode leads 11 and 12 are formed at the opposite ends of the battery cell such that the electrode leads 11 and 12 are positioned on the same axis and the electrode leads 11 and 12 are positioned in the middle of the battery cell 13. Consequently, the pouch-shaped battery 10 is constructed in a symmetrical structure.
A sheathing member 14 is a two-unit member including upper and lower sheathing parts. While an electrode assembly (not shown) is received in a location part 15 defined in the sheathing member 14, the contact regions of the sheathing member 14, i.e., the opposite sides 14a, the upper ends 14b, and the lower ends 14c of the sheathing member 14 are bonded to each other. In this way, pouch-shaped battery 10 is manufactured. The sheathing member 14 is constructed in a laminate structure including a resin layer/a metal film layer/a resin layer. Consequently, it is possible to bond the opposite sides 14a and the upper and lower ends 14b and 14c of the upper and lower sheathing parts of the sheathing member 14, which are in contact with each other, to each other by applying heat and pressure to the opposite sides 14a and the upper and lower ends 14b and 14c of the upper and lower sheathing parts of the sheathing member 14 so as to weld the resin layers to each other. According to circumstances, the opposite sides 14a and the upper and lower ends 14b and 14c of the upper and lower sheathing parts of the sheathing member 14 may be bonded to each other using a bonding agent. For the opposite sides 14a of the sheathing member 14, the same resin layers of the upper and lower sheathing parts of the sheathing member 14 are in direct contact with each other, whereby uniform sealing at the opposite sides 14a of the sheathing member 14 is accomplished by welding. For the upper and lower ends 14b and 14c of the sheathing member 14, on the other hand, the electrode leads 11 and 12 protrude from the upper and lower ends 14b and 14c of the sheathing member 14. For this reason, the upper and lower ends 14b and 14c of the upper and lower sheathing parts of the sheathing member 14 are thermally welded to each other, while a film-shaped sealing member 16 is interposed between the electrode leads 11 and 12 and the sheathing member 14, in consideration of the thickness of the electrode leads 11 and 12 and the difference in material between the electrode leads 11 and 12 and the sheathing member 14, so as to increase sealability.
When viewing the vertical section of the pouch-shaped battery 10, the battery cell 13 is positioned on the central axis of the battery. That is to say, an upper location part 15a and a lower location part 15b protrude from the central axis of the battery to the same thickness.
FIG. 3 is a typical view illustrating a battery module constructed by electrically connecting a plurality of pouch-shaped batteries, one of which 10 is shown in FIG. 1.
Referring to FIG. 3, a plurality of batteries 10, 10a, 10b, and 10c are arranged on the same plane in a module case, and the batteries 10, 10a, 10b, and 10c are electrically connected with each other via corresponding bus bars 22. In this way, a battery module 20 is constructed. The length of bus bars 22 is decided depending upon the distance between the corresponding electrode terminals 11 and 12a of the two neighboring batteries 10 and 10a. When the length of the bus bars 22 is increased, the inner resistance of the battery module is also increased, and therefore, the performance of the battery module is lowered. Consequently, in order to reduce the resistance due to the connection between the batteries 10 and 10a, i.e., in order to reduce the length of the bus bars 22, there have been proposed some conventional arts for increasing the width of the electrode terminals 11, 12, 11a and 12a. However, the increase of the electrode terminal width to the battery width ratio increases the possibility of short circuits during the assembly of the battery module.
Furthermore, no bus bar 22 is provided between the electrode terminals 12a and 11b of the battery module shown in FIG. 3, i.e., a dead space (DS) exists between electrode terminals 12a and 11b. In consideration of the size of the batteries 10a and 10b, and the size and the position of the electrode terminals 12 and 11b, however, the dead space is limited to be utilized for a special purpose. In consideration of the fact that the necessity of a battery pack constructed in a compact structure while providing the same capacity and output becomes high, research into a battery module structure utilizing the dead space is also required.
In order to efficiently construct the battery module using the pouch-shaped battery 10 having the structure shown in FIG. 1 as a unit cell, it is necessary that the unit cells 10a, 10b, 10c, and 10d are arranged in the lateral direction (in the horizontal direction) as shown in FIG. 3. This is because, when the unit cells 10a, 10b, 10c, and 10d are arranged in the thickness direction (in the vertical direction), the connection of connecting members, such as the bus bars, for electrically connecting the unit cells 10a, 10b, 10c, and 10d is difficult. When the vertically disposed electrode terminals are to be electrically connected with each other, not the plate-shaped bus bars but three-dimensional connecting members are necessary. In this case, a welding process for connection is troublesome and complicated.
In addition, the pouch-shaped battery 10 as shown in FIG. 1 has a small thickness, and therefore, the pouch-shaped batteries are arranged only in the horizontal direction, whereby the mechanical strength of the battery module is very small. For this reason, it is necessary to use a strong member, such as a cartridge, in order to increase the mechanical strength.